I don't understand Apple users. They continue putting out crappy products and their users act like they've been personally hurt and there's nothing they can do about it.
There is something you can do about it: buy someone else's computer. How long has it been since you used anything else?
HTTP is not designed for persistent connections (WebSockets were hacked on later, but JMAP does not use them anyway). This turns a push protocol into a poll protocol, which is a stark regression. It's also got all sorts of other crap built-in which is really not necessary for this use-case but which an intrepid implementer will have to deal with regardless.
JSON does not cope well with binary data, which is common in emails. It fails to elegantly deal with the various email encodings which exist in the wild. Consider as well that all JSON numbers are floating point numbers, despite the fact that floating point numbers provide absolutely nothing of value to this spec and in fact are more likely to introduce bugs than not. And embedded devices can't deal with floats quickly or elegantly, but still need to implement them if they want to use JSON-based protocols. And for what gain!
In short, JMAP reinvents the wheel but worse for the sake of making it easier for web developers to build web shit around email. This kind of stupid change for change's sake is an epidemic in the webshit scene. IMAP is warty but it's fine. Let it be. When your only hammer is JavaScript, everyone else's thumb looks like a nail.
Though I have no complaints about the way they went about implementing it (open standards hooray!), as a mail client author and someone with lots of experience with mail in general - I'm NACK to JMAP. I think that it comes with some questionable design decisions (HTTP? JSON?) which on their face I imagine look fine to the typical HNer, but in many ways is a regression from IMAP. I would prefer to see the limitations of IMAP addressed with a few carefully written extensions to the spec - which is already extensible and has a thriving set of useful extensions in the wild.
By no means is IMAP a particularly good protocol, but it is extremely broadly supported and designed more with email in mind than JMAP appears to be, which seems to focus more on bringing shiny web tech to email regardless of its utility in such a context. It's also one of many closely interlinked mail-related specifications, and JMAP fails to integrate well with many related specs imo.
You might appreciate the sourcehut approach (which I am the author of). Each build job is decoupled from git and can be submitted ad-hoc with zero or more git repos declared in the manifest. Your manifest is machine-editable too so you can add extra build steps or tweak various options before submitting it in specific cases. postmarketOS does this, for example, to automate builds of all of their packages. SourceHut itself does this to fill the demand made by this trend, too, by pulling build manifests out of your git repo and tweaking the sources to check out specific commits, then submitting it over the API.
As I understand it, most sellers have their public keys available from several sources and savvy buyers will cross-verify them. It would probably raise too much suspicion of LE swapped out the keys and there was a discrepancy with the cross-references.
The story of how Mew (Pokemon) came to be is also pretty interesting. From memory: when they were getting close to shipping, they had a completely full cart (only one or two bytes to spare). They removed all of the debugging stuff, which freed up enough space for a new Pokemon to be defined. A programmer secretly added Mew right before they shipped, and Nintendo didn't find out until a couple of weeks later.
There is something you can do about it: buy someone else's computer. How long has it been since you used anything else?